The present invention generally relates to a braking apparatus, and more specifically to a self-adjusting braking apparatus.
Hydraulically actuated brakes operate by applying a volume of pressurized fluid against a piston. The piston urges a disk attached to a shaft against a reaction member attached to a fixed structure. Friction between the disk and the reaction member causes the rotation of the shaft to slow or stop. Repeated application of the brakes causes wear on the surface of the disk which increases the distance which the piston must travel in order to slow the shaft. This increased distances requires a greater volume of pressurized fluid to be applied to the piston to create the same frictional force.
A disadvantage to requiring a greater volume of pressurized fluid to actuate the brake is that a larger master cylinder is required to supply the pressurized fluid. This larger cylinder can increase the cost of the braking system. This volume increase could be avoided simply by not forcing the piston to retract form the friction disks when actuation pressure is removed. The resulting close clearances between the brake surfaces, however, would cause significant energy to be lost to friction and viscous forces when braking is not being performed. The brake clearances could also be manually adjusted as the brake surfaces wear, reducing the volume of pressurized fluid required and thus the size of the required master cylinder. However, manual adjustment of the piston position is costly, labor intensive, and time consuming. In addition, estimating the rate of wear of the friction material is difficult, making the timing of the brake adjustment difficult to predict.
What is needed therefore is a self-adjusting braking apparatus which overcomes the above-mentioned drawbacks.
In accordance with a first aspect of the present invention, there is provided a brake apparatus including a brake disk secured to a shaft and a reaction plate secured to a housing. The brake apparatus further includes a fluid actuated piston which urges the brake disk against the reaction plate to slow rotation of the shaft and an adjustment member positioned by the piston. The brake apparatus yet further includes a spring interposed between the adjustment member and the piston. The piston positions the adjustment member relative to the brake disk when fluid is applied to said piston. The spring urges the piston away from the adjustment member and brake disk when fluid pressure is removed from the piston.
In accordance with a second aspect of the present invention, there is provided a method of operating a brake apparatus having a brake disk secured to a shaft, a reaction plate secured to a housing, a fluid actuated piston which urges the brake disk against the reaction plate to slow rotation of the shaft, an adjustment member positioned by the piston, and a spring interposed between the adjustment member and the piston. The method includes the steps of positioning the adjustment member relative to the brake disk by applying fluid to the piston, and urging the piston away from the adjustment member and brake disk with the spring when fluid pressure is removed from the piston.
The invention further provides a brake apparatus including a brake disk driven by a shaft, a reaction plate secured to a housing and a selectively moveable piston having a contact surface engageable with the brake disk wherein the brake disk is urged against the reaction plate to slow rotation of the shaft in response to compressive movement of the piston. An adjustment member is provided between the piston and the reaction member and is operable to: (i) urge the piston away from the brake disk in response to deactivation of the brake assembly, and (ii) readjust a gap clearance between the brake disk and at least one of the piston and the reaction member in response to brake wear.